Fix -Wsign-compare compiler warnings

Comparing signed and unsigned integer expressions can have unexpected
results because the signed integer will get promoted to an unsigned
integer. To avoid the warning, add an explicit cast to the unsigned
type, along with a check to catch negative values.

examples/dctool_parse.c

@@ -152,7 +152,7 @@ dctool_parse_run (int argc, char *argv[], dc_context_t *context, dc_descriptor_t
 		goto cleanup;
 	}
 
-	for (unsigned int i = 0; i < argc; ++i) {
+	for (int i = 0; i < argc; ++i) {
 		// Read the input file.
 		buffer = dctool_file_read (argv[i]);
 		if (buffer == NULL) {

examples/output_raw.c

@@ -80,7 +80,7 @@ mktemplate_datetime (char *buffer, size_t size, dc_parser_t *parser)
 	n = snprintf (buffer, size, "%04i%02i%02iT%02i%02i%02i",
 		datetime.year, datetime.month, datetime.day,
 		datetime.hour, datetime.minute, datetime.second);
-	if (n < 0 || n >= size)
+	if (n < 0 || (size_t) n >= size)
 		return -1;
 
 	return n;
@@ -92,7 +92,7 @@ mktemplate_number (char *buffer, size_t size, unsigned int number)
 	int n = 0;
 
 	n = snprintf (buffer, size, "%04u", number);
-	if (n < 0 || n >= size)
+	if (n < 0 || (size_t) n >= size)
 		return -1;
 
 	return n;

src/context.c

@@ -77,7 +77,7 @@ l_vsnprintf (char *str, size_t size, const char *format, va_list ap)
 	 * enough.
 	 */
 	n = vsnprintf (str, size, format, ap);
-	if (n >= size)
+	if (n >= 0 && (size_t) n >= size)
 		n = -1;
 #endif
 

src/hw_ostc3.c

@@ -1024,7 +1024,7 @@ hw_ostc3_firmware_readline (FILE *fp, dc_context_t *context, unsigned int addr,
 	unsigned char ascii[39];
 	unsigned char faddr_byte[3];
 	unsigned int faddr = 0;
-	int n = 0;
+	size_t n = 0;
 
 	if (size > 16) {
 		ERROR (context, "Invalid arguments.");

src/suunto_d9.c

@@ -261,7 +261,8 @@ suunto_d9_device_packet (dc_device_t *abstract, const unsigned char command[], u
 	}
 
 	// Verify the size of the package.
-	if (array_uint16_be (answer + 1) + 4 != asize) {
+	unsigned int len = array_uint16_be (answer + 1);
+	if (len + 4 != asize) {
 		ERROR (abstract->context, "Unexpected answer size.");
 		return DC_STATUS_PROTOCOL;
 	}

src/suunto_eonsteel_parser.c

@@ -137,7 +137,6 @@ static const struct {
 
 static enum eon_sample lookup_descriptor_type(suunto_eonsteel_parser_t *eon, struct type_desc *desc)
 {
-	int i;
 	const char *name = desc->desc;
 
 	// Not a sample type? Skip it
@@ -160,7 +159,7 @@ static enum eon_sample lookup_descriptor_type(suunto_eonsteel_parser_t *eon, str
 	name += 8;
 
 	// .. and look it up in the table of sample type strings
-	for (i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
+	for (size_t i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
 		if (!strcmp(name, type_translation[i].name))
 			return type_translation[i].type;
 	}
@@ -179,8 +178,7 @@ static parser_sample_event_t lookup_event(const char *name, const eon_event_t ev
 
 static const char *desc_type_name(enum eon_sample type)
 {
-	int i;
-	for (i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
+	for (size_t i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
 		if (type == type_translation[i].type)
 			return type_translation[i].name;
 	}

src/suunto_vyper2.c

@@ -252,7 +252,8 @@ suunto_vyper2_device_packet (dc_device_t *abstract, const unsigned char command[
 	}
 
 	// Verify the size of the package.
-	if (array_uint16_be (answer + 1) + 4 != asize) {
+	unsigned int len = array_uint16_be (answer + 1);
+	if (len + 4 != asize) {
 		ERROR (abstract->context, "Unexpected answer size.");
 		return DC_STATUS_PROTOCOL;
 	}

src/usbhid.c

@@ -777,7 +777,7 @@ dc_usbhid_write (dc_iostream_t *abstract, const void *data, size_t size, size_t
 
 out:
 #ifdef _WIN32
-	if (nbytes > size) {
+	if ((size_t) nbytes > size) {
 		WARNING (abstract->context, "Number of bytes exceeds the buffer size (" DC_PRINTF_SIZE " > " DC_PRINTF_SIZE ")!", nbytes, size);
 		nbytes = size;
 	}